Application of new strategies to reduce suspended solids in zero-exchange system: I.Histological alterations in the gills of Nile tilapia

摘要

An 8-week experiment was conducted for evaluating new strategies to reduce suspended solids in zeroexchange system and using Nile tilapia gills alterations as criteria for the evaluation. An experimental design with six treatments and three replicates per treatment was performed. Four heterotrophic-based system (HS) treatments; daily feeding at normal rates without application of fasting and/ or settling strategies (CH), daily feeding at normal rates and application of settling solid strategy (SH), the amount of feed delivered in full amount but on alternate day without settling (FH), the amount of feed delivered in full amount but on alternate day with application of settling strategy (SFH) and two autotrophic-based system (AS) treatments (daily feeding at normal rates without application of fasting and/or settling strategies (CA), the amount of feed delivered in full amount but on alternate day without settling (FH). Fish reared under SH and SFH treatments had fewer and less severe histopathological lesions in gills than controls and fasting treatments. The observed pathologic gill lesions were; partial or complete fusion of some lamellae and damage in the chloride cells. The most severe gill morphological alterations were observed in the fish reared under FA and FH treatment, the observed pathologic gill lesions were; epithelial lifting of secondary lamella, necrosis, fusion of some filaments, filament disorganization, hypertrophy and hyperplasia of the lamellar epithelial cells with partial or complete fusion of some lamellae, rupture of lamellar epithelium, increase of mucus secretion , aneurysm in the primary and secondary lamella, congestion of the blood vessels and damage of chloride cell damage. Our study demonstrate that settling treatments may consider as an effective strategy to reduce the stress imposed on the fish and to protect the aquatic habitats under zero-exchange systems and only a maximum concentration of 220-250 mg SS/1 is recommended as a guideline.